A pigment masterbatch is a solid or liquid additive that is used for coloring a polymer composition. The masterbatch is a highly concentrated mixture of pigments and other components. The masterbatch is added to a polymer composition before and/or during extrusion of the polymer composition to obtain a colored polymer composition.
Masterbatches are described in, for example WO 2012/084865 and WO 2009/010673. WO 2012/084865 describes a masterbatch consisting of pigment and a mold release agent. The mold release agent is selected from the group consisting of low-molecular weight polyolefin oils, low-molecular weight polyolefin waxes, montan waxes and aliphatic or aromatic carboxylic acid esters of fatty acids and/or fatty alcohols.
WO 2009/010673 describes a process for the manufacturing of a masterbatch comprising the production of a mixture comprising at least one binder, at least one additive and/or at least one pigment and the pelletizing of said mixture. The binder can be chosen from several commercial waxes comprising alcohols or amides. Ethylene bis stearamide waxes are mentioned as an example.
In the prior art two types of pigment masterbatches are known. So called dry (or solid) masterbatches, which are in the form of powders or pellets, and so called liquid masterbatches, which are in the form of liquids. Dosing the dry masterbatches with a polymer composition to an extruder is relatively easy. However dosing a liquid masterbatch to a polymer composition in an extruder is cumbersome, gives rise to fouling of the working area and screw slip may occur, especially at higher loadings of liquid masterbatches. Furthermore liquid masterbatches tend to form agglomerates with flakes and/or powder resulting in clogging of the process equipment.
The pigment masterbatches of the prior art have a number of further disadvantages. In practice, for coloring different polymer compositions different pigment masterbatches must be prepared. Also coloring with pigment masterbatches can give the problem of non-uniform color distribution in the extrudate. Another problem is the change from one masterbatch to a different masterbatch on processing equipment. During this change cleaning of the equipment is necessary and cleaning of the equipment tends to take hours of time while making a lot of waste product.